The tread of a tire is commonly provided with various features that can improve performance as well as impact the aesthetics of the tread. For example, a tread may include blocks of tread and/or ribs; grooves along the lateral and circumferential directions, and/or apertures of various sizes. These features can improve tread wear, handling, braking, consumer appeal and other characteristics of the tire as well.
A sipe is another feature that is frequently applied to a tire tread. As used herein, a sipe is a groove in the tread that is less than 2 mm in width. In addition to tire aesthetics, sipes can be used to improve e.g., wet and snow traction. For example, sipes of various sizes and orientations may be added to the ribs and/or blocks of a tire in varying configurations to improve the ability of the tire to grip the road surface in rain or snow. However, sipes typically increase the rolling resistance of a tire particularly as the tire tread becomes less rigid through the addition of sipes. This effect can be countered in part by decreasing the width of the individual sipes manufactured into the tread.
In a conventional approach, sipes are added to the tire during the curing process. More specifically, first an uncured tire (i.e. a green tire) is created on a tire forming drum in a layered process where sheets of material are added in steps along with other components such as e.g., the bead cores, belts, and/or other components. A tread band is provided for a tread region. The materials are sequentially applied to a forming drum that initially provides a flat surface but ultimately moves the beads together to form the toroidal tire shape.
The resulting green tire is then placed into a curing press where heat and pressure are used to cure the tire rubber components as well as bond the rubber components together. During this curing step, the walls of the press can be equipped with intricate molding elements that impart sipes into the uncured tread of the green tire. For example, fin-like metal projections may be added to the walls of the tire press in the tread forming section in order to impart sipes and other details to the tread as the tread is cured by pressure and heat.
The conventional manufacture of a tire with a sipes along the tread presents certain challenges. The nature of the molding process limits the shape and configuration of sipes that can be added to the tire tread using the insertion of the fin-like metal projections on the walls of the curing press. The conventional tire press can create sipes that extend from the outer surface of the tread inward, but cannot create sipes in the tire tread that appear only after a period of tread wear has occurred, i.e. hidden sipes. Similarly, sipes can be created that extend radially outward from the innermost portion of the tread but conventional methods cannot create, a sipe that is hidden from the bottom and top portion of the tread—i.e. conventional methods cannot create a sipe that does not extend from either the radially innermost or radially outermost surface of the tread. In addition, the manufacture of very thin sipes using standard molding techniques is fraught with difficulties due to the fragility of mold elements like cores and/or fins needed to make such sipes.
Accordingly, a tire and a method of making a tire having sipes would be useful. More particularly, a method that can be used to construct a tire having sipes of very thin widths and/or hidden sipes would be particularly beneficial. Such a method that can also be used to create sipes of varying geometries, densities, and depths while still allowing for control of the rigidity of the tire tread so as to improve rolling resistance would also be useful.